Re-tasking balloons in a balloon network based on expected failure modes of balloons

ABSTRACT

Example methods and systems for assigning tasks to balloons within a balloon network are described. One example system includes a first sub-fleet of balloons assigned a first set of one or more tasks within a balloon network, a second sub-fleet of balloons assigned a second set of one or more tasks within the balloon network, and a control system configured to determine that a first balloon in the first sub-fleet of balloons initially has a predicted failure mode that corresponds to the first set of tasks, subsequently determine that the first balloon has a predicted failure mode that corresponds to the second set of tasks, and reassign the first balloon from the first sub-fleet of balloons to the second sub-fleet of balloons.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Computing devices such as personal computers, laptop computers, tabletcomputers, cellular phones, and countless types of Internet-capabledevices are increasingly prevalent in numerous aspects of modern life.As such, the demand for data connectivity via the Internet, cellulardata networks, and other such networks, is growing. However, there aremany areas of the world where data connectivity is still unavailable, orif available, is unreliable and/or costly. Accordingly, additionalnetwork infrastructure is desirable.

SUMMARY

Example methods and systems for assigning tasks to balloons within aballoon network are described. An example system may include a firstsub-fleet of balloons that is assigned a first set of one or more taskswithin the network. The system may also include a second sub-fleet ofballoons assigned a second set of one or more tasks. A control systemmay be configured to determine that a first balloon in the firstsub-fleet of balloons initially has a predicted failure mode thatcorresponds to the first set of tasks. The control system maysubsequently determine that the first balloon has a predicted failuremode that corresponds to the second set of tasks. The control system maythen reassign the first balloon from the first sub-fleet of balloons tothe second sub-fleet of balloons.

In one example, a system is provided that includes a first sub-fleet ofballoons assigned a first set of one or more tasks within a balloonnetwork, a second sub-fleet of balloons assigned a second set of one ormore tasks within the balloon network, and a control system configuredto determine that a first balloon in the first sub-fleet of balloonsinitially has a predicted failure mode that corresponds to the first setof tasks, subsequently determine that the first balloon has a predictedfailure mode that corresponds to the second set of tasks, and reassignthe first balloon from the first sub-fleet of balloons to the secondsub-fleet of balloons.

In another example, a method is provided that includes determining thata first balloon in a balloon network has a predicted failure mode thatcorresponds to a first set of tasks, where the balloon network includesat least a first sub-fleet of balloons assigned a first set of one ormore tasks and a second sub-fleet of balloons assigned a second set ofone or more tasks, subsequently determining that the first balloon has apredicted failure mode that corresponds to the second set of tasks, andreassigning the first balloon from the first sub-fleet of balloons tothe second sub-fleet of balloons.

In still another example, a system is provided that includes a pluralityof sub-fleets of balloons, where each sub-fleet of balloons is assigneda corresponding set of one or more tasks within a balloon network andwhere each balloon in one of the sub-fleets of balloons initially has apredicted failure mode that corresponds to the set of tasks assigned tothe sub-fleet of balloons, and a control system configured toperiodically determine that a particular balloon in a first sub-fleet ofballoons has a predicted failure mode that corresponds to a set of tasksassigned to a second sub-fleet of balloons and reassign the particularballoon from the first sub-fleet of balloons to the second sub-fleet ofballoons.

In yet another example, a system may include means for determining thata first balloon in a balloon network has a predicted failure mode thatcorresponds to a first set of tasks, where the balloon network includesat least a first sub-fleet of balloons assigned a first set of one ormore tasks and a second sub-fleet of balloons assigned a second set ofone or more tasks, means for subsequently determining that the firstballoon has a predicted failure mode that corresponds to the second setof tasks, and means for reassigning the first balloon from the firstsub-fleet of balloons to the second sub-fleet of balloons.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram illustrating an example balloon network.

FIG. 2 is a block diagram illustrating an example balloon-networkcontrol system.

FIG. 3 shows a high-altitude balloon according to an example embodiment.

FIG. 4 is a simplified block diagram illustrating a balloon network thatincludes super-nodes and sub-nodes, according to an example embodiment.

FIG. 5 is a block diagram of a method, according to an exampleembodiment.

FIG. 6A illustrates two sub-fleets of balloons within a balloon network,according to an example embodiment.

FIG. 6B illustrates a predicted failure mode of a balloon within one ofthe sub-fleets of balloons from FIG. 6A, according to an exampleembodiment.

FIG. 6C illustrates reassignment of a balloon within one of thesub-fleets of balloons from FIG. 6A, according to an example embodiment.

FIG. 6D illustrates the sub-fleets of balloons following thereassignment of FIG. 6C, according to an example embodiment.

FIG. 7A illustrates three sub-fleets of balloons within a balloonnetwork, according to an example embodiment.

FIG. 7B illustrates predicted failure modes of balloons within thesub-fleets of balloons of FIG. 7A, according to an example embodiment.

FIG. 7C illustrates reassignment of balloons within the sub-fleets ofballoons of FIG. 7A, according to an example embodiment.

FIG. 7D illustrates the sub-fleets of balloons following thereassignment of FIG. 7C, according to an example embodiment.

FIG. 8 shows flight paths of two different sub-fleets of balloons,according to an example embodiment.

FIG. 9 illustrates a failure rate curve, according to an exampleembodiment.

DETAILED DESCRIPTION

I. Overview

Examples of methods and systems are described herein. It should beunderstood that the words “example” and “exemplary” are used herein tomean “serving as an example, instance, or illustration.” Any embodimentor feature described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other embodiments orfeatures. The example or exemplary embodiments described herein are notmeant to be limiting. It will be readily understood that certain aspectsof the disclosed systems and methods can be arranged and combined in awide variety of different configurations, all of which are contemplatedherein.

Furthermore, the particular arrangements shown in the Figures should notbe viewed as limiting. It should be understood that other embodimentsmay include more or less of each element shown in a given Figure.Further, some of the illustrated elements may be combined or omitted.Yet further, an exemplary embodiment may include elements that are notillustrated in the Figures.

Examples herein may be configured to help provide control of a datanetwork that includes a plurality of balloons, for example, configuredas a mesh network formed by high-altitude balloons deployed in thestratosphere. In some examples, the network of balloons may be dividedinto multiple sub-fleets of balloons. Each sub-fleet of balloons may begiven different tasks within the network. For instance, one sub-fleet ofballoons may provide local service to ground-based stations, anothersub-fleet of balloons may serve as relay nodes between balloons, whileanother sub-fleet of balloons may be sent to provide service onlong-distance flight paths, and so on. Additionally, each sub-fleet ofballoons may be operated according to a separate set of constraints.

In further examples, a control system may assign individual balloons tosub-fleets. Additionally, balloons may be assigned to multiple differentsub-fleets during their lifetimes. For instance, a balloon may be placedin a sub-fleet that allows the balloon to execute long-distance flightpaths during a first period of the balloon's life. The balloon may thenbe reassigned to a second sub-fleet where the balloon may serve as arelay node between other network balloons during a second stage of theballoon's life. The balloon may be reassigned again to a third sub-fleetat a later point in time, where the balloon may serve as a weatherballoon that collects data for weather forecasting. Other exampleballoon life stages exist as well.

In some examples, a control system may assign individual balloons tosub-fleets based on predicted failure modes of the individual balloons.A predicted failure mode of a balloon may indicate how and when theballoon may be expected to fail. More specifically, a failure mode of aballoon may indicate a certain type of failure of an individual ballooncomponent. For instance, components that may fail may include balloonenvelopes, communication systems, propelling systems, power systems,sensor systems, or other mechanical or electrical systems. Some failuremodes may render the balloon entirely non-functional, while otherfailure modes may only make the balloon unusable for certain purposes.For instance, a balloon envelope may experience a small hole that maylead to a slow loss of pressure but the balloon may still be functionalfor some time, or the balloon may experience a rip in the envelope thatmay cause rapid balloon descent.

The control system may use predicted failure modes of individualballoons to determine what tasks may be most appropriate for a balloonto handle within the network. For example, if it is determined that aspecific component of a balloon may be likely to fail soon, the balloonmay be re-tasked to carry out different functions that don't require thecomponent. For instance, it may be determined that a balloon that iscarrying out tasks that require the balloon to spend time at highaltitudes is likely to experience a failure in its envelope.Accordingly, the balloon may be reassigned to handle less demandingtasks. As another example, it may be determined that a balloon that isserving as a relay balloon may likely experience a failure in itscommunication systems with other balloons. The balloon may be reassignedto serve as a weather balloon, which may not require the same amount ofballoon-to-balloon communication. The control system may execute othertypes of reassignments based on predicted failure modes as well.

Additionally, the predicted failure modes of individual balloons mayalso be used to position balloons or sub-fleets of balloons inparticular locations. For instance, if it is determined that an envelopeof an individual balloon is likely to fail soon, the balloon may beassigned to a sub-fleet of balloons that stays close to a particularground-based station. Accordingly, the balloon may be recovered easilyif it does fail as predicted. Furthermore, a sub-fleet containingballoons that may be likely to fail soon may be controlled so thatindividual failing balloons don't cross commercial flight lanes, land onpopulated areas, or land in areas where the balloons may be difficult torecover.

In additional examples, predicted failure modes of individual balloonsmay include more complex metrics. For instance, a predicted failure modemay include separate times-to-failure of multiple different componentsor types of failure. In further examples, a failure of a certaincomponent or a certain type of failure that is likely to occur at theearliest point in time may be determined. Additionally, a probabilitydistribution of times-to-failure, or a failure rate curve, may bedetermined for entire balloons or balloon components as well or instead.

In some examples, balloons and/or balloon components may experience ahigh likelihood of failure during an initial period shortly after theballoon is launched. After surviving this initial period, the likelihoodof failure may drop substantially for a long period of time until thelikelihood of failure slowly starts to increase as the balloon getsolder. An example control system may take advantage of such failure ratecurves. For instance, balloons may be assigned to a first sub-fleetduring an initial period where the balloon undergoes one or more stresstests. The first sub-fleet may not perform any functions vital to thenetwork to minimize the harm done if the balloon fails. After survivingthe initial period, the balloon may then be reassigned to a secondsub-fleet. Because the balloon may be unlikely to fail at that point,the balloon may be given more important tasks within the secondsub-fleet.

Example methods therefore may allow control systems to assign tasks toindividual balloons operating within a balloon network. Balloons may bedivided into sub-fleets based on predicted failure modes of theballoons, among other things. The sub-fleets may each carry outdifferent tasks that are coordinated to facilitate functioning of theballoon network.

II. Example Balloon Networks

In order that the balloons can provide a reliable data network in thestratosphere, where winds may affect the locations of the variousballoons in an asymmetrical manner, the balloons in an exemplary networkmay be configured move latitudinally and/or longitudinally relative toone another by adjusting their respective altitudes, such that the windcarries the respective balloons to the respectively desired locations.

Further, in an exemplary balloon network, the balloons may communicatewith one another using free-space optical communications. For instance,the balloons may be configured for optical communications usingultrabright LEDs or possibly lasers for optical signaling (althoughregulations for laser communications may restrict laser usage). Inaddition, the balloons may communicate with ground-based station(s)using radio-frequency (RF) communications.

In some embodiments, a high-altitude-balloon network may be homogenous.More specifically, in a homogenous high-altitude-balloon network, eachballoon is configured to communicate with nearby balloons via free-spaceoptical links. Further, some or all of the balloons in such a network,may also be configured communicate with ground-based station(s) using RFcommunications. (Note that in some embodiments, the balloons may behomogenous in so far as each balloon is configured for free-spaceoptical communication with other balloons, but heterogeneous with regardto RF communications with ground-based stations.)

In other embodiments, a high-altitude-balloon network may beheterogeneous, and thus may include two or more different types ofballoons. For example, some balloons may be configured as super-nodes,while other balloons may be configured as sub-nodes. (Note also thatsome balloons may be configured to function as both a super-node and asub-node.)

In such a configuration, the super-node balloons may be configured tocommunicate with nearby super-node balloons via free-space opticallinks. However, the sub-node balloons may not be configured forfree-space optical communication, and may instead be configured for,e.g., RF communications. Accordingly, a super-node may be furtherconfigured to communicate with nearby sub-nodes using RF communications.The sub-nodes may accordingly relay communications from the super-nodesto ground-based station(s) using RF communications. Configured as such,the super-nodes may collectively function as backhaul for the balloonnetwork, while the sub-nodes function to relay communications from thesuper-nodes to ground-based stations.

FIG. 1 is a simplified block diagram illustrating a balloon network 100,according to an exemplary embodiment. As shown, balloon network 100includes balloons 102A to 102E, which are configured to communicate withone another via free-space optical links 104. Configured as such,balloons 102A to 102E may collectively function as a mesh network forpacket-data communications. Further, balloons 102A to 102D may beconfigured for RF communications with ground-based stations 106 via RFlinks 108.

In an exemplary embodiment, balloons 102A to 102E are high-altitudeballoons, which are deployed in the stratosphere. At moderate latitudes,the stratosphere includes altitudes between approximately 10 kilometers(km) and 50 km altitude above the surface. At the poles, thestratosphere starts at an altitude of approximately 8 km. In anexemplary embodiment, high-altitude balloons may be generally configuredto operate in an altitude range within the stratosphere that has lowerwinds (e.g., between 5 and 20 miles per hour (mph)).

More specifically, in a high-altitude-balloon network, balloons 102A to102E may generally be configured to operate at altitudes between 17 kmand 22 km (although other altitudes are possible). This altitude rangemay be advantageous for several reasons. In particular, this layer ofthe stratosphere generally has mild wind and turbulence (e.g., windsbetween 5 and 20 miles per hour (mph)). Further, while the winds between17 km and 22 km may vary with latitude and by season, the variations canbe modeled in a reasonably accurate manner. Additionally, altitudesabove 17 km are typically above the maximum flight level designated forcommercial air traffic. Therefore, interference with commercial flightsis not a concern when balloons are deployed between 17 km and 22 km.

To transmit data to another balloon, a given balloon 102A to 102E may beconfigured to transmit an optical signal via an optical link 104. In anexemplary embodiment, a given balloon 102A to 102E may use one or morehigh-power light-emitting diodes (LEDs) to transmit an optical signal.Alternatively, some or all of balloons 102A to 102E may include lasersystems for free-space optical communications over optical links 104.Other types of free-space optical communication are possible. Further,In order to receive an optical signal from another balloon via anoptical link 104, a given balloon 102A to 102E may include one or moreoptical receivers. Additional details of balloons implementations arediscussed in greater detail below, with reference to FIG. 3.

In a further aspect, balloons 102A to 102D may utilize one or more ofvarious different RF air-interface protocols for communicationground-based stations 106 via RF links 108. For instance, some or all ofballoons 102A to 102D may be configured to communicate with ground-basedstations 106 using protocols described in IEEE 802.11 (including any ofthe IEEE 802.11 revisions), various cellular protocols such as GSM,CDMA, UMTS, EV-DO, WiMAX, and/or LTE, and/or one or more proprietyprotocols developed for balloon-to-ground RF communication, among otherpossibilities.

In a further aspect, there may scenarios where RF links 108 do notprovide a desired link capacity for balloon-to-ground communications.For instance, increased capacity may be desirable to provide backhaullinks from a ground-based gateway, and in other scenarios as well.Accordingly, an exemplary network may also include downlink balloons,which provide a high-capacity air-to-ground link.

For example, in balloon network 100, balloon 102E is configured as adownlink balloon. Like other balloons in an exemplary network, adownlink balloon 102E may be operable for optical communication withother balloons via optical links 104. However, a downlink balloon 102Emay also be configured for free-space optical communication with aground-based station 112 via an optical link 110. Optical link 110 maytherefore serve as a high-capacity link (as compared to an RF link 108)between the balloon network 100 and a ground-based station 108.

Note that in some implementations, a downlink balloon 102E mayadditionally be operable for RF communication with ground-based stations106. In other cases, a downlink balloon 102E may only use an opticallink for balloon-to-ground communications. Further, while thearrangement shown in FIG. 1 includes just one downlink balloon 102E, anexemplary balloon network can also include multiple downlink balloons.On the other hand, a balloon network can also be implemented without anydownlink balloons.

In other implementations, a downlink balloon may be equipped with aspecialized, high-bandwidth RF communication system forballoon-to-ground communications, instead of or in addition to afree-space optical communication system. The high-bandwidth RFcommunication system may take the form of an ultra-wideband system,which provides an RF link with substantially the same capacity as theoptical links 104. Other forms are also possible.

Ground-based stations, such as ground-based stations 106 and/or 108, maytake various forms. Generally, a ground-based station may includecomponents such as transceivers, transmitters, and/or receivers forcommunication via RF links and/or optical links with a balloon network.Further, a ground-based station may use various air-interface protocolsin order communicate with a balloon 102A to 102E over an RF link 108. Assuch, a ground-based station 106 may be configured as an access pointsvia which various devices can connect to balloon network 100.Ground-based stations 106 may have other configurations and/or serveother purposes without departing from the scope of the invention.

Further, some ground-based stations, such as ground-based station 108,may be configured as gateways between balloon network 100 and one ormore other networks. Such a ground-based station 108 may thus serve asan interface between the balloon network and the Internet, a cellularservice provider's network, and/or other types of networks. Variationson this configuration and other configurations of a ground-based station108 are also possible.

A. Mesh-Network Functionality

As noted, balloons 102A to 102E may collectively function as a meshnetwork. More specifically, since balloons 102A to 102E may communicatewith one another using free-space optical links, the balloons maycollectively function as a free-space optical mesh network.

In a mesh-network configuration, each balloon 102A to 102E may functionas a node of the mesh network, which is operable to receive data directto it and to route data to other balloons. As such, data may be routedfrom a source balloon to a destination balloon by determining anappropriate sequence of optical links between the source balloon and thedestination balloon. These optical links may be collectively referred toas a “lightpath” for the connection between the source and destinationballoons. Further, each of the optical links may be referred to as a“hop” on the lightpath.

Further, in order to operate as a mesh network, balloons 102A to 102Emay employ various routing techniques and self-healing algorithms. Insome embodiments, a balloon network 100 may employ adaptive or dynamicrouting, where a lightpath between a source and destination balloon isdetermined and set-up when the connection is needed, and released at alater time. Further, when adaptive routing is used, the lightpath may bedetermined dynamically depending upon the current state, past state,and/or predicted state of the balloon network.

In addition, the network topology may change as the balloons 102A to102E move relative to one another and/or relative to the ground.Accordingly, an exemplary balloon network 100 may apply a mesh protocolto update the state of the network as the topology of the networkchanges. For example, to address the mobility of the balloons 102A to102E, balloon network 100 may employ and/or adapt various techniquesthat are employed in mobile ad hoc networks (MANETs). Other examples arepossible as well.

In some implementations, a balloon network 100 may be configured as atransparent mesh network. More specifically, in a transparent balloonnetwork, the balloons may include components for physical switching thatis entirely optical, without any electrical involved in physical routingof optical signals. Thus, in a transparent configuration with opticalswitching, signals travel through a multi-hop lightpath that is entirelyoptical.

In other implementations, the balloon network 100 may implement afree-space optical mesh network that is opaque. In an opaqueconfiguration, some or all balloons 102A to 102E may implementoptical-electrical-optical (OEO) switching. For example, some or allballoons may include optical cross-connects (OXCs) for OEO conversion ofoptical signals. Other opaque configurations are also possible.

In a further aspect, balloons in an exemplary balloon network 100 mayimplement wavelength division multiplexing (WDM), which may help toincrease link capacity. When WDM is implemented with transparentswitching, physical lightpaths through the balloon network may besubject to the “wavelength continuity constraint.” More specifically,because the switching in a transparent network is entirely optical, itmay be necessary to assign the same wavelength for all optical links ona given lightpath.

An opaque configuration, on the other hand, may avoid the wavelengthcontinuity constraint. In particular, balloons in an opaque balloonnetwork may include the OEO switching systems operable for wavelengthconversion. As a result, balloons can convert the wavelength of anoptical signal at each hop along a lightpath.

Further, various routing algorithms may be employed in an opaqueconfiguration. For example, to determine a primary lightpath and/or oneor more diverse backup lightpaths for a given connection, exemplaryballoons may apply or consider shortest-path routing techniques such asDijkstra's algorithm and k-shortest path, and/or edge and node-diverseor disjoint routing such as Suurballe's algorithm, among others.Additionally or alternatively, techniques for improving QoS may beemployed when determining a lightpath. Other techniques are alsopossible.

B. Station-Keeping Functionality

In an exemplary embodiment, a balloon network 100 may implementstation-keeping functions to help provide a desired network topology.For example, station-keeping may involve each balloon 102A to 102Emaintaining and/or moving into a certain position relative to one ormore other balloons in the network (and possibly in a certain positionrelative to the ground). As part of this process, each balloon 102A to102E may implement station-keeping functions to determine its desiredpositioning within the desired topology, and if necessary, to determinehow to move to the desired position.

The desired topology may vary depending upon the particularimplementation. In some cases, balloons may implement station-keeping toprovide a substantially uniform topology. In such case, a given balloon102A to 102E may implement station-keeping functions to position itselfat substantially the same distance (or within a certain range ofdistances) from adjacent balloons in the balloon network 100.

In other cases, a balloon network 100 may have a non-uniform topology.For instance, exemplary embodiments may involve topologies whereballoons are distributed more or less densely in certain areas, forvarious reasons. As an example, to help meet the higher bandwidthdemands that are typical in urban areas, balloons may be clustered moredensely over urban areas. For similar reasons, the distribution ofballoons may be denser over land than over large bodies of water. Manyother examples of non-uniform topologies are possible.

In a further aspect, the topology of an exemplary balloon network may bedynamic and adaptable. In particular, station-keeping functionality ofexemplary balloons may allow the balloons to adjust their respectivepositioning in accordance with a change in the desired topology of thenetwork. For example, one or more balloons could move to new positionsto increase or decrease the density of balloons in a given area.Further, in some embodiments, balloons may be in continuous or nearlycontinuous motion, and station-keeping may involve moving balloons so asto try to meet certain requirements for e.g., coverage in various areas.

In some embodiments, a balloon network 100 may employ an energy functionto determine if and/or how balloons should move to provide a desiredtopology. In particular, the state of a given balloon and the states ofsome or all nearby balloons may be input to an energy function. Theenergy function may apply the current states of the given balloon andthe nearby balloons to a desired network state (e.g., a statecorresponding to the desired topology). A vector indicating a desiredmovement of the given balloon may then be determined by determining thegradient of the energy function. The given balloon may then determineappropriate actions to take in order to effectuate the desired movement.For example, a balloon may determine an altitude adjustment oradjustments such that winds will move the balloon in the desired manner.

C. Control of Balloons in a Balloon Network

In some embodiments, mesh networking and/or station-keeping functionsmay be centralized. For example, FIG. 2 is a block diagram illustratinga balloon-network control system, according to an exemplary embodiment.In particular, FIG. 2 shows a distributed control system, which includesa central control system 200 and a number of regional control-systems202A to 202B. Such a control system may be configured to coordinatecertain functionality for balloon network 204, and as such, may beconfigured to control and/or coordinate certain functions for balloons206A to 206I.

In the illustrated embodiment, central control system 200 may beconfigured to communicate with balloons 206A to 206I via number ofregional control systems 202A to 202C. These regional control systems202A to 202C may be configured to receive communications and/oraggregate data from balloons in the respective geographic areas thatthey cover, and to relay the communications and/or data to centralcontrol system 200. Further, regional control systems 202A to 202C maybe configured to route communications from central control system 200 tothe balloons in their respective geographic areas. For instance, asshown in FIG. 2, regional control system 202A may relay communicationsand/or data between balloons 206A to 206C and central control system200, regional control system 202B may relay communications and/or databetween balloons 206D to 206F and central control system 200, andregional control system 202C may relay communications and/or databetween balloons 206G to 206I and central control system 200.

In order to facilitate communications between the central control system200 and balloons 206A to 206I, certain balloons may be configured asdownlink balloons, which are operable to communicate with regionalcontrol systems 202A to 202C. Accordingly, each regional control system202A to 202C may be configured to communicate with the downlink balloonor balloons in the respective geographic area it covers. For example, inthe illustrated embodiment, balloons 204A, 204D, and 204H are configuredas downlink balloons. As such, regional control systems 202A to 202C mayrespectively communicate with balloons 204A, 204D, and 204H via opticallinks 206, 208, and 210, respectively.

In the illustrated configuration, where only some of balloons 206A to206I are configured as downlink balloons, the balloons 206A, 206D, and206H that are configured as downlink balloons may function to relaycommunications from central control system 200 to other balloons in theballoon network, such as balloons 206B, 206C, 206E to 206G, and 206I.However, it should be understood that it in some implementations, it ispossible that all balloons may function as downlink balloons. Further,while FIG. 2 shows multiple balloons configured as downlink balloons, itis also possible for a balloon network to include only one downlinkballoon.

Note that a regional control system 202A to 202B may in fact just beparticular type of ground-based station that is configured tocommunicate with downlink balloons (e.g., such as ground-based station112 of FIG. 1). Thus, while not shown in FIG. 2, the control systemshown in FIG. 2 may be implemented in conjunction with other types ofground-based stations (e.g., access points, gateways, etc.).

In a centralized control arrangement, such as that shown in FIG. 2, thecentral control system 200 (and possibly regional control systems 202Ato 202C as well) may coordinate certain mesh-networking functions forballoon network 204. For example, balloons 206A to 206I may send thecentral control system 200 certain state information, which the centralcontrol system 200 may utilize to determine the state of balloon network204. The state information from a given balloon may include locationdata, optical-link information (e.g., the identity of other balloonswith which the balloon has established an optical link, the bandwidth ofthe link, wavelength usage and/or availability on a link, etc.), winddata collected by the balloon, and/or other types of information.Accordingly, the central control system 200 may aggregate stateinformation from some or all the balloons 206A to 206I in order todetermine an overall state of the network.

The overall state of the network may then be used to coordinate and/orfacilitate certain mesh-networking functions such as determininglightpaths for connections. For example, the central control system 200may determine a current topology based on the aggregate stateinformation from some or all the balloons 206A to 206I. The topology mayprovide a picture of the current optical links that are available inballoon network and/or the wavelength availability on the links. Thistopology may then be sent to some or all of the balloons so that arouting technique may be employed to select appropriate lightpaths (andpossibly backup lightpaths) for communications through the balloonnetwork 204.

In a further aspect, the central control system 200 (and possiblyregional control systems 202A to 202C as well) may also coordinatecertain station-keeping functions for balloon network 204. For example,the central control system 200 may input state information that isreceived from balloons 206A to 206I to an energy function, which mayeffectively compare the current topology of the network to a desiredtopology, and provide a vector indicating a direction of movement (ifany) for each balloon, such that the balloons can move towards thedesired topology. Further, the central control system 200 may usealtitudinal wind data to determine respective altitude adjustments thatmay be initiated to achieve the movement towards the desired topology.The central control system 200 may provide and/or support otherstation-keeping functions as well.

As noted, FIG. 2 shows a distributed-control arrangement, with regionalcontrol systems 202A to 202C coordinating communications between acentral control system 200 and a balloon network 204. Such anarrangement may be useful in a balloon network that covers a largegeographic area. In some embodiments, a distributed control system mayeven support a global balloon network that provides coverage everywhereon earth. Of course, a distributed-control arrangement may be useful inother scenarios as well.

Further, it should be understood that other control-system arrangementsare possible. For instance, some implementations may involve adistributed control system with additional layers (e.g., sub-regionsystems within the regional control systems, and so on). Alternatively,control functions may be provided by a single, centralized, controlsystem, which communicates directly with one or more downlink balloons.

In a further aspect, control and coordination of a balloon network maybe shared between a ground-based control system and a balloon network tovarying degrees, depending upon the implementation. In fact, in someembodiments, there may be no ground-based control system. In such anembodiment, all network control and coordination functions may beimplemented by the balloon network itself. For example, certain balloonsmay be configured to provide the same or similar functions as centralcontrol system 200 and/or regional control systems 202A to 202C. Otherexamples are also possible.

Furthermore, control and/or coordination of a balloon network may bede-centralized. For example, each balloon may relay state informationto, and receive state information from, some or all nearby balloons.Further, each balloon may relay state information that it receives froma nearby balloon to some or all nearby balloons. When all balloons doso, each balloon may be able to individually determine the state of thenetwork. Alternatively, certain balloons may be designated to aggregatestate information for a given portion of the network. These balloons maythen coordinate with one another to determine the overall state of thenetwork.

Further, in some aspects, control of a balloon network may be partiallyor entirely localized, such that it is not dependent on the overallstate of the network. For example, individual balloons may implementstation-keeping functions that only consider nearby balloons. Inparticular, each balloon may implement an energy function that takesinto account its own state and the states of nearby balloons. The energyfunction may be used to maintain and/or move to a desired position withrespect to the nearby balloons, without necessarily considering thedesired topology of the network as a whole. However, when each balloonimplements such an energy function for station-keeping, the balloonnetwork as a whole may maintain and/or move towards the desiredtopology.

D. Illustrative Balloon Configurations

Various types of balloon systems may be incorporated in an exemplaryballoon network. As noted above, an exemplary embodiment may utilizehigh-altitude balloons, which typically operate in an altitude rangebetween 17 km and 22 km. FIG. 3 is a simplified block diagramillustrating a high-altitude balloon 300, according to an exemplaryembodiment. As shown, the balloon 300 includes an envelope 302, a skirt304, a payload 306, and a cut-down system 308 that is attached betweenthe balloon 302 and payload 304.

The envelope 302 and skirt 304 may take various forms, which may becurrently well-known or yet to be developed. For instance, the envelope302 and/or skirt 304 may be made of a highly-flexible latex material ormay be made of a rubber material such as chloroprene. Other materialsare also possible. Further, the shape and size of the envelope 302 andskirt 304 may vary depending upon the particular implementation.Additionally, the envelope 302 may be filled with various differenttypes of gases, such as helium and/or hydrogen. Other types of gases arepossible as well.

The payload 306 of balloon 300 may include a processor 312 and on-boarddata storage, such as memory 314. The memory 314 may take the form of orinclude a non-transitory computer-readable medium. The non-transitorycomputer-readable medium may have instructions stored thereon, which canbe accessed and executed by the processor 312 in order to carry out theballoon functions described herein.

The payload 306 of balloon 300 may also include various other types ofequipment and systems to provide a number of different functions. Forexample, payload 306 may include optical communication system 316, whichmay transmit optical signals via an ultra-bright LED system 320, andwhich may receive optical signals via an optical-communication receiver322 (e.g., a photo-diode receiver system). Further, payload 306 mayinclude an RF communication system 318, which may transmit and/orreceive RF communications via an antenna system 324. The payload 306 mayalso include a power supply 326 to supply power to the variouscomponents of balloon 300.

Further, payload 306 may include various types of other systems andsensors 328. For example, payload 306 may include one or more videoand/or still cameras, a GPS system, various motion sensors (e.g.,accelerometers, gyroscopes, and/or compasses), and/or various sensorsfor capturing environmental data. Further, some or all of the componentswithin payload 306 may be implemented in a radiosonde, which may beoperable to measure, e.g., pressure, altitude, geographical position(latitude and longitude), temperature, relative humidity, and/or windspeed and/or direction, among other information.

As noted, balloon 306 includes an ultra-bright LED system 320 forfree-space optical communication with other balloons. As such, opticalcommunication system 316 may be configured to transmit a free-spaceoptical signal by modulating the ultra-bright LED system 320. Theoptical communication system 316 may be implemented with mechanicalsystems and/or with hardware, firmware, and/or software. Generally, themanner in which an optical communication system is implemented may vary,depending upon the particular application.

In a further aspect, balloon 300 may be configured for altitude control.For instance, balloon 300 may include a variable buoyancy system, whichis configured to change the altitude of the balloon 300 by adjusting thevolume and/or density of the gas in the balloon 300. A variable buoyancysystem may take various forms, and may generally be any system that canchange the volume and/or density of gas in envelope 302.

In an exemplary embodiment, a variable buoyancy system may include abladder 310 that is located inside of envelope 302. The buoyancy of theballoon 300 may therefore be adjusted by changing the density and/orvolume of the gas in bladder 310. To change the density in bladder 310,balloon 300 may be configured with systems and/or mechanisms for heatingand/or cooling the gas in bladder 310. Further, to change the volume,balloon 300 may include pumps or other features for adding gas to and/orremoving gas from bladder 310. Additionally or alternatively, to changethe volume of bladder 310, balloon 300 may include release valves orother features that are controllable to allow air to escape from bladder310.

Further, the balloon 300 may include a navigation system (not shown).The navigation system may implement station-keeping functions tomaintain position within and/or move to a position in accordance with adesired topology. In particular, the navigation system may usealtitudinal wind data to determine altitudinal adjustments that resultin the wind carrying the balloon in a desired direction and/or to adesired location. The altitude-control system may then make adjustmentsto the density of the balloon chamber in order to effectuate thedetermined altitudinal adjustments and cause the balloon to movelaterally to the desired direction and/or to the desired location.

Alternatively, the altitudinal adjustments may be computed by aground-based control system and communicated to the high-altitudeballoon. As another alternative, the altitudinal adjustments may becomputed by a ground-based or satellite-based control system andcommunicated to the high-altitude balloon. Furthermore, in someembodiments, specific balloons in a heterogeneous balloon network may beconfigured to compute altitudinal adjustments for other balloons andtransmit the adjustment commands to those other balloons.

As shown, the balloon 300 also includes a cut-down system 308. Thecut-down system 308 may be activated to separate the payload 306 fromthe rest of balloon 300. This functionality may be utilized anytime thepayload needs to be accessed on the ground, such as when it is time toremove balloon 300 from a balloon network, when maintenance is due onsystems within payload 306, and/or when power supply 326 needs to berecharged or replaced.

In an alternative arrangement, a balloon may not include a cut-downsystem. In such an arrangement, the navigation system may be operable tonavigate the balloon to a landing location, in the event the balloonneeds to be removed from the network and/or accessed on the ground.Further, it is possible that a balloon may be self-sustaining, such thatit theoretically does not need to be accessed on the ground.

Note that movement and locations of balloons, such as balloon 300, canvary since winds in the stratosphere may affect the locations of theballoons in a differential manner. A balloon in an example network maybe configured to change its horizontal position by adjusting itsvertical position (i.e., altitude). For example, by adjusting itsaltitude, a balloon may be able to find winds that will carry theballoon horizontally (e.g., latitudinally and/or longitudinally) to adesired horizontal location. Wind speed and/or direction may vary withaltitude, and since current wind velocities as well as weather forecastsare available, in principle, a balloon may be directed to a location byidentifying an altitude at which a wind direction takes a balloon toalong a desired trajectory. However, a balloon without other forms ofpropulsion may be constrained to follow the wind and there may not be asingle altitude with winds taking the balloon along the desiredtrajectory. In addition, to control a fleet of balloons, movement of theballoons should occur from one location above the surface of the Earthto another in a predictable manner.

E. Example Heterogeneous Network

In some embodiments, a high-altitude-balloon network may includesuper-node balloons, which communicate with one another via opticallinks, as well as sub-node balloons, which communicate with super-nodeballoons via RF links. Generally, the optical links between super-nodeballoons have more bandwidth than the RF links between super-node andsub-node balloons. As such, the super-node balloons may function as thebackbone of the balloon network, while the sub-nodes may providesub-networks providing access to the balloon network and/or connectingthe balloon network to other networks.

FIG. 4 is a simplified block diagram illustrating a balloon network thatincludes super-nodes and sub-nodes, according to an exemplaryembodiment. More specifically, FIG. 4 illustrates a portion of a balloonnetwork 400 that includes super-node balloons 410A to 410C (which mayalso be referred to as “super-nodes”) and sub-node balloons 420 (whichmay also be referred to as “sub-nodes”).

Each super-node balloon 410A to 410C may include a free-space opticalcommunication system that is operable for packet-data communication withother super-node balloons. As such, super-nodes may communicate with oneanother over optical links. For example, in the illustrated embodiment,super-node 410A and super-node 401B may communicate with one anotherover optical link 402, and super-node 410A and super-node 401C maycommunicate with one another over optical link 404.

Each of the sub-node balloons 420 may include a radio-frequency (RF)communication system that is operable for packet-data communication overone or more RF air interfaces. Accordingly, each super-node balloon 410Ato 410C may include an RF communication system that is operable to routepacket data to one or more nearby sub-node balloons 420. When a sub-node420 receives packet data from a super-node 410, the sub-node 420 may useits RF communication system to route the packet data to a ground-basedstation 430 via an RF air interface.

As noted above, the super-nodes 410A to 410C may be configured for bothlonger-range optical communication with other super-nodes andshorter-range RF communications with nearby sub-nodes 420. For example,super-nodes 410A to 410C may use using high-power or ultra-bright LEDsto transmit optical signals over optical links 402, 404, which mayextend for as much as 100 miles, or possibly more. Configured as such,the super-nodes 410A to 410C may be capable of optical communications atspeeds of 10 to 50 GB/sec.

A larger number of balloons may then be configured as sub-nodes, whichmay communicate with ground-based Internet nodes at speeds on the orderof approximately 10 MB/sec. Configured as such, the sub-nodes 420 may beconfigured to connect the super-nodes 410 to other networks and/or toclient devices.

Note that the data speeds and link distances described in the aboveexample and elsewhere herein are provided for illustrative purposes andshould not be considered limiting; other data speeds and link distancesare possible.

In some embodiments, the super-nodes 410A to 410C may function as a corenetwork, while the sub-nodes 420 function as one or more access networksto the core network. In such an embodiment, some or all of the sub-nodes420 may also function as gateways to the balloon network 400.Additionally or alternatively, some or all of ground-based stations 430may function as gateways to balloon network 400.

III. Example Methods

FIG. 5 is a block diagram of a method, according to an exampleembodiment. The method 500 may be carried out by a control system of aballoon network. For example, some or all of method 500 may be carriedout by a central control system and/or regional systems such as the onesdescribed above with respect to FIG. 2. The control system(s) maycommunicate with the balloons within the balloon network. In furtherexamples, all or some of method 500 may be carried out by one or morecomputing systems located on the individual balloons. In some examples,the parts of the method 500 may be combined, separated into additionalparts, and/or carried out in a different order than shown. Otherconfigurations are also possible.

More specifically, the method 500 may involve determining that a firstballoon in a balloon network has a predicted failure mode thatcorresponds to a first set of tasks, as shown by block 502. The balloonnetwork may have a first sub-fleet of balloons assigned the first set oftasks and a second sub-fleet of balloons assigned a second set of tasks.The method 500 may further involve subsequently determining that thefirst balloon has a predicted failure mode that corresponds to thesecond set of tasks, as shown by block 504. The method 500 may furtherinvolve reassigning the first balloon from the first sub-fleet ofballoons to the second sub-fleet of balloons, as shown by block 506.

A balloon network may have a first sub-fleet of balloons assigned afirst set of tasks and a second sub-fleet of balloons assigned a secondset of tasks. A sub-fleet of balloons may be a group of balloonsoperating according to a certain set of constraints within the balloonnetwork. The constraints may be used to position individual balloonswithin a sub-fleet and/or assign tasks to individual balloons. Certainconstraints may be applied to multiple sub-fleets (or every sub-fleet)while other constraints may be used only for one specific sub-fleet.Additionally, in some examples, different sub-fleets may containballoons of different types, which may have different shapes, sizes,equipment, etc.

Furthermore, each sub-fleet may be assigned a particular set of tasksthat facilitate functioning of the network as a whole. For instance, asub-fleet of balloons may be assigned to provide local service to aground-based station. The balloons in the sub-fleet may communicate withone or more ground-based stations using RF communications. In someexamples, the balloons in the sub-fleet may be positioned around asingle station. In other examples, the balloons may be controlled tomove between stations and provide service to multiple stations. Theballoons may also send and receive information to and/or from balloonsfrom other sub-fleets, and then use their RF communication systems toroute the data to and/or from ground-based stations.

In another example, a sub-fleet of balloons may be assigned to serve asrelay balloons between balloons from other sub-fleets. For instance, theballoons may be assigned to relay information to and from other balloonsusing free-space optical communication systems. Balloons within thesub-fleet may be positioned so that large gaps within the network may beavoided. Accordingly, the sub-fleet may facilitate communication betweendistant groups of balloons by serving as relay nodes within the network.

In a further example, a sub-fleet of balloons may be assigned to executelong-distance flight paths. A network of balloons may benefit fromhaving certain balloons that can travel long distances to provideservice to particular locations. For instance, an event drawing a largecrowd may require additional balloons to provide the needed amount ofcoverage. Balloons from a sub-fleet of balloons assigned to cover longdistances can be sent to the location to provide the needed services.

In another example, a sub-fleet of balloons may be assigned to collectdata for weather forecasting. Balloons can be positioned where weatherdata is needed (e.g., for planning flight paths of other balloons).Sensors on the balloons may be used to collect data about currentweather conditions. The balloons may then transmit the data to the restof the network, for instance by sending the data to relay balloons or toballoons that can transmit the data to ground-based stations.

FIG. 6A shows two sub-fleets of balloons, according to an exampleembodiment. Balloons 602, 604, 606 may be part of a first sub-fleet,sub-fleet A, which may be assigned a first set of tasks. Balloons 608,610, 612 may be part of a second sub-fleet, sub-fleet B, which may beassigned a second set of tasks. Each sub-fleet may be assigned or moreof the tasks described above, as well as other types of tasks notexplicitly described above.

Method 500 may involve determining that a first balloon in a balloonnetwork has a predicted failure mode that corresponds to the first setof tasks that is assigned to the first sub-fleet, as shown by block 502.A predicted failure mode may indicate how and when a balloon is expectedto fail. A predicted failure mode may correspond with a set of tasks ifa balloon may be able to perform some or all of the tasks even if thepredicted mode of failure occurs. In other examples, a predicted failuremode may correspond with a set of tasks if the set of tasks contains themost appropriate task or tasks for the balloon to perform within thenetwork after factoring in the balloon's predicted mode of failure.

For instance, a balloon may have a predicted failure mode indicatingthat the balloon's RF communication systems used to communicate withground-based stations may be likely to fail. This predicted failure modemay correspond with a set of tasks assigned to a particular sub-fleet ofballoons—for instance, a sub-fleet that serves as relay nodes betweenother balloons. The free-space optical communication systems of aballoon that are used to communicate with other balloons may not beaffected by a failure of the balloon's RF communication systems.Accordingly, a balloon with this predicted failure mode may be able toperform tasks assigned to the sub-fleet of relay balloons even if theballoon fails as expected.

In some examples, a predicted failure mode may include an expectedfailure of a particular balloon component. For instance, it may bedetermined that the balloon may be likely to experience a failure in anenvelope, a communication system, a propelling system, a power system, asensor system and/or another mechanical or electrical system.Additionally, a predicted failure mode may include a time-to-failure ofan individual component and/or of the entire balloon.

In other examples, a predicted failure mode may include a specific typeof failure of a given component. For instance, some types of failuresmay be instantly catastrophic, such as when a balloon envelope bursts.Other types of failures may be slow-acting, taking days or months oryears to progress to complete failure. For instance, a balloon mayexperience a small leak, but may still be able to operate within thenetwork for a significant period of time.

Many other examples of different types of failures of balloon componentsexist as well. In some examples, certain balloon systems, such as aballoon's sensor systems, may only partially fail. For instance, aballoon may lose certain weather sensors (such as thermometers orbarometers) while retaining other weather sensors (such as moisturesensors or wind gauges). In such an example, a predicted failure modemay include partial failures. In other examples, a predicted failuremode may be a type of failure that is likely to occur at the earliestpoint in time from a group of multiple different types of failure.

In further examples, partial failures may include intermittent failuresor balloons with reduced capability. For instance, a balloonexperiencing a partial failure may generate less solar power, have lesspower storage available in batteries, have less vertical rangeavailable, need more power for maneuvers, have lower communicationsbitrates, or take longer to establish optical communications links. Someexample systems may differentiate between fully-capable balloons,slightly impaired balloons, highly impaired balloons, and so on. Inadditional examples, a failure mode may indicate a failure relative tosome threshold level. For instance, a failure mode may incorporateballoons failing to generate X watts of solar power for one or morechosen values of X.

Method 500 may further involve subsequently determining that the firstballoon has a predicted failure mode that corresponds to a second set oftasks that is assigned to the second sub-fleet, as shown by block 504.For instance, a balloon may develop a new predicted failure mode afterfunctioning in a certain role for a period of time. Systems orcomponents of the balloon that have been used heavily may become morelikely to fail over time. Predictions about likely failure modes can bemade based on data received by active sensors located on a balloonand/or based on failures of similar balloons or balloons that carriedout similar tasks, among other factors. Based on the new predictedfailure mode, a new set of tasks may be more appropriate for the balloonto perform.

FIG. 6B shows a predicted failure mode, according to an exampleembodiment. As an example, balloon 606 of sub-fleet A may develop apredicted failure mode indicating that the balloon's free-space opticalcommunication systems used for communication with other balloons may belikely to fail soon. Balloons in sub-fleet A may be assigned to serve asrelay nodes between other balloons. Accordingly, balloons in sub-fleet Amay rely heavily on their free-space optical communication systems tocommunicate with other balloons. The predicted failure mode of balloon606 may now correspond with a set of tasks that doesn't require heavyuse of the free-space optical communication systems. For instance,balloon 606 may be more appropriately placed in sub-fleet B, which maybe assigned to collect data for weather forecasting. Even if some ofballoon 606's communication systems fail, the balloon may still havefunctioning sensors that can collect the needed weather data.Accordingly, the tasks assigned to sub-fleet B may now be moreappropriate for balloon 606 to fulfill within the network.

Method 500 may further involve reassigning the first balloon from thefirst sub-fleet of balloons to the second sub-fleet of balloons, asshown by block 506. After determining that a particular balloon may bebetter suited to perform tasks assigned to a different sub-fleet, theballoon may be reassigned to maximize its utility within the network.The decision to reassign a balloon may come from a control system, whichmay be a central control system or a localized control system asdescribed above, and in either case, could be implemented in one or moreground-based stations, one or more balloons, or a combination of one ormore ground-based stations and one or more balloons.

FIG. 6C shows the reassignment of a balloon, according to an exampleembodiment. After determining that the predicted failure mode of balloon606 corresponds better with the set of tasks assigned to sub-fleet B,the balloon 606 may be reassigned from sub-fleet A to sub-fleet B. FIG.6D shows the sub-fleets following the reassignment of balloon 606. Theballoon 606 may now carry out the tasks assigned to sub-fleet B, whichmay provide more utility to the network given the balloon's predictedfailure mode.

In some examples, a control system may periodically move balloonsbetween multiple sub-fleets of balloons based on predicted failure modesof individual balloons and/or based on other factors. The control systemmay balance the distribution of balloons across different sub-fleetsover time to facilitate functioning of the entire network and tomaximize the utility of individual balloons. For instance, the controlsystem may periodically determine that a certain sub-fleet does not haveenough balloons to carry out its tasks. For example, the sub-fleet mayhave lost some balloons due to failure and/or the demand for the tasksassigned to the sub-fleet may have increased. The control system maythen reassign additional balloons to the sub-fleet.

In additional examples, a priority level associated with each set oftasks may be determined. For instance, some tasks may be more vital tothe functioning of the overall network than other tasks. The controlsystem may take into account the priority level associated with taskscarried out by different sub-fleets when assigning balloons. Forexample, the control system may first ensure that sub-fleets carryingout higher priority tasks have enough balloons with sufficientcapabilities first. Once the higher priority tasks are covered, thecontrol system may then assign balloons to sub-fleets carrying out lowerpriority tasks to the extent that the network has enough balloons tofulfill the lower priority tasks as well.

FIG. 7A illustrates three sub-fleets of balloons within a balloonnetwork, according to an example embodiment. A first sub-fleet,sub-fleet A, may contain balloons 702, 704, and 706. Sub-fleet A may beassigned tasks that tend to cause wear and tear to balloon envelopes,such as spending significant time at high altitudes. A second sub-fleet,sub-fleet B, may contain balloons 708, 710, and 712. Sub-fleet B may beassigned tasks that rely heavily on the balloons' free-space opticalcommunication systems, such as serving as relay nodes between otherballoons within the network. A third sub-fleet, sub-fleet C, may containballoons 714, 716, and 718. Sub-fleet C may be assigned tasks that tendto make extensive use of the balloons' propelling systems, such ascarrying out long-distance flight paths.

A control system may periodically determine predicted failure modes ofindividual balloons within one or more of the sub-fleets of balloons.FIG. 7B shows predicted failure modes of individual balloons, accordingto an example embodiment. Balloon 706, a balloon from sub-fleet A, mayhave a predicted failure mode indicating that the envelope of balloon706 may be likely to fail soon. For instance, strain sensors located onthe balloon may detect significant deformity in the material of theballoon envelope. As another example, the prediction may be based onpast failures of similar balloons. For instance, it may be determinedthat balloon envelopes may be likely to fail after spending a certainamount of time at high altitudes. Predictions could be based on acombination of factors as well.

Additionally, as shown in FIG. 7B, balloon 710, a balloon from sub-fleetB, may have a predicted failure mode indicating that balloon 710'sfree-space optical communication systems may be likely to fail soon. Forinstance, balloon 710 may have made extensive use of itsballoon-to-balloon communication systems while serving as a relay nodewithin sub-fleet B. Based on the history of the balloon's activitiesand/or diagnostic systems located on the balloon, it may be determinedthat a failure of the balloon's communication systems may be imminent.

Furthermore, as shown in FIG. 7B, balloon 714, a balloon from sub-fleetC, may have a predicted failure mode indicating that balloon 714'spropelling systems may be likely to experience a failure. Balloon 714may have relied heavily on its propelling systems while carrying outnumerous long-distance flight paths as part of sub-fleet C.Consequently, a prediction may be made that if balloon 714 continues toexecute long-distance flight paths, the balloon's propelling systems maybe likely to fail in the near future.

After determining predicted failure modes of one or more balloons, acontrol system may reassign balloons between sub-fleets. FIG. 7C showsthe reassignment of three balloons, according to an example embodiment.Balloon 706 from sub-fleet A may have a predicted failure modeindicating that the balloon's envelope may be likely to fail. It may bedetermined that balloon 706 is better suited to tasks that don't causeheavy stress to balloon envelopes. Consequently, balloon 706 may bereassigned to sub-fleet B, which may be assigned to serve as relay nodeswithin the balloon network. By serving as a relay node, balloon 706'senvelope may be preserved, possibly extending the useful functioning ofballoon 706 within the network.

Additionally, balloon 710 from sub-fleet B may have a predicted failuremode indicating that one or more of the balloon's communications systemsmay be likely to fail. If balloon 710 continues to serve as a relay nodewithin sub-fleet B, it may be determined that a failure of the balloon'scommunication systems may be likely. Balloon 710 may be moreappropriately placed in a sub-fleet that doesn't rely as extensively ona balloon's communication systems. Therefore, balloon 710 may bereassigned to sub-fleet C, which may be assigned to carry outlong-distance flight paths.

Furthermore, balloon 714 from sub-fleet C may have a predicted failuremode indicating that one or more of the balloon's propelling systems maybe likely to fail. Balloon 714 may no longer be able to carry outlong-distance flight paths within sub-fleet C. Consequently, balloon 714may be reassigned to sub-fleet A, which may be assigned tasks that areless demanding on a balloon's propelling systems.

FIG. 7D shows the three sub-fleets of balloons following thereassignments of FIG. 7C, according to an example embodiment. As shown,balloon 706 has been reassigned from sub-fleet A to sub-fleet B, balloon710 has been reassigned from sub-fleet B to sub-fleet C, and balloon 714has been reassigned from sub-fleet C to sub-fleet A. Accordingly, thenetwork may be able to maximize the utility of each balloon and in somecases, extend the functioning life of individual balloons by leveragingpredictions about balloon failures. Additionally, in some examples, someor all of the balloons may go through life stages and may be assigneddifferent tasks in each life stage.

In other examples, balloons may be reassigned to sub-fleets that operatein different regions based on predicted failure modes. For instance,balloons that can no longer generate solar power as rapidly orefficiently may be assigned to sub-fleets that allow the balloons towork in regions with more sunlight. In another example, if a balloon'sthermal regulation system is impaired, the balloon may be assigned towork in warmer regions and/or the balloon may be assigned lower-powertasks, leaving more power for heating. In yet another example, a balloonwith a partially failing battery that can no longer store as much powermay be assigned to daytime work with only low-power work at night (i.e.,avoiding high speed communication or altitude control maneuvers atnight).

In some examples, sub-fleets may be assigned to carry out differentlength flight paths based on predicted failure modes. FIG. 8 showsflight paths of two different sub-fleets of balloons, according to anexample embodiment. A first sub-fleet of balloons may contain balloons802, 804, and 806. The dotted lines represent the flight paths of theballoons. As shown, the first sub-fleet may stay within a certainsection of one or more countries. A second sub-fleet may containballoons 808, 810, 812. As shown by the dotted lines, the secondsub-fleet may be assigned to carry out longer flight paths, such aspaths across an ocean between continents. As balloons develop predictedfailure modes over time, they may be reassigned to sub-fleets that carryout less demanding flight paths. For instance, balloons may be movedfrom the second sub-fleet of balloons to the first sub-fleet balloonsover time.

In additional examples, systems and methods may be used to facilitateballoon recovery when predicted failure modes indicate likely failuresof entire balloons. For instance, it may be determined that anindividual balloon is likely to experience an imminent total failure,such as a rip in the balloon envelope. Accordingly, the balloon may bemoved to a sub-flight that may be assigned to an area where the ballooncan easily be recovered. For example, the balloon may be rerouted toavoid bodies of water or countries where balloon recovery may bedifficult. Further, the balloon may be repositioned to avoid landing onpopulated locations or to avoid crossing commercial flight lanes. Theballoon may also be moved to a location close to a ground-based stationso that data can be quickly offloaded from the failing balloon, and soon.

In additional examples, a predicted failure mode of a balloon mayinclude a probability distribution of failures, or a failure rate curve.FIG. 9 shows a failure rate curve 902, according to an exampleembodiment. As shown, a particular balloon component or the entireballoon may be likely to fail very early during a first period 904 of aballoon's lifetime. However, if the component or balloon survives theinitial period 904, the probability of failure may drop to a low levelduring a second period 906 of the balloon's lifetime. The probability offailure may then begin to rise during a third period 908 much later inthe balloon's lifetime as the balloon gets older. Accordingly, apredicted failure mode may include probabilities of failures atdifferent times, or other metrics. Furthermore, a failure rate curve 902may be determined for individual balloon components, entire balloons, orparticular types of failures, for example.

In further examples, a control system may use a failure rate curve likethe one in FIG. 9 to assign particular balloons to sub-fleets. Forinstance, if a balloon is likely to have a high rate of failure early inits lifetime, the balloon may first be placed in a sub-fleet that isassigned tasks that are not vital to the functioning of the network as awhole. If the balloon survives the initial period where the risk offailure is high, the balloon may then be reassigned to a sub-fleet thatcarries out more important functions. In some examples, balloons mayfirst be assigned to a sub-fleet that exposes the balloons to one ormore stress tests. The stress tests may be designed to uncover flaws ina balloon's construction that may lead to early balloon failure. If theballoon survives the stress tests, the balloon may then be reassigned toa different sub-fleet to carry out tasks within the network. A controlsystem may leverage failure rate curves of individual balloons and/orballoon components in other ways as well.

In further examples, predictions about balloons failures andreassignment decisions may be improved over time as more informationabout past balloons becomes available. In some examples, a computingsystem may apply a machine-learning process to improve associationsbetween certain predicted failure modes and corresponding tasks withinthe network. In addition to the general techniques discussed herein, thecomputing device may apply any of a number of well-known machinelearning processes such as an artificial neural network (ANN), SVM(Support Vector Machines), Genetic Algorithms, Bayesian inference, BayesNets, a Reinforcement Learning method, regression analysis, or aDecision Tree, for instance. After performing such a machine-learningprocess, a computing system may then be able to conclude that certaincorrelations between predicted failure modes and assigned tasks areinaccurate or could be more accurate, and then update the predictionsand/or assignments accordingly.

It should be understood that the simplified examples given here are notmeant to be limiting. In practice, control systems may use the disclosedsystems and methods to predict a wide variety of types of possiblefailures, and assign balloons to a number of different tasksaccordingly. Additionally, the systems and methods described herein maybe used to assign tasks to balloons based on predicted balloon failuresin a variety of different types of network of balloons.

IV. Conclusion

Further, the above detailed description describes various features andfunctions of the disclosed systems, devices, and methods with referenceto the accompanying figures. In the figures, similar symbols typicallyidentify similar components, unless context dictates otherwise. Theexample embodiments described herein and in the figures are not meant tobe limiting. Other embodiments can be utilized, and other changes can bemade, without departing from the spirit or scope of the subject matterpresented herein. It will be readily understood that the aspects of thepresent disclosure, as generally described herein, and illustrated inthe figures, can be arranged, substituted, combined, separated, anddesigned in a wide variety of different configurations, all of which areexplicitly contemplated herein.

With respect to any or all of the ladder diagrams, scenarios, and flowcharts in the figures and as discussed herein, each block and/orcommunication may represent a processing of information and/or atransmission of information in accordance with example embodiments.Alternative embodiments are included within the scope of these exampleembodiments. In these alternative embodiments, for example, functionsdescribed as blocks, transmissions, communications, requests, responses,and/or messages may be executed out of order from that shown ordiscussed, including substantially concurrent or in reverse order,depending on the functionality involved. Further, more or fewer blocksand/or functions may be used with any of the ladder diagrams, scenarios,and flow charts discussed herein, and these ladder diagrams, scenarios,and flow charts may be combined with one another, in part or in whole.

A block that represents a processing of information may correspond tocircuitry that can be configured to perform the specific logicalfunctions of a herein-described method or technique. Alternatively oradditionally, a block that represents a processing of information maycorrespond to a module, a segment, or a portion of program code(including related data). The program code may include one or moreinstructions executable by a processor for implementing specific logicalfunctions or actions in the method or technique. The program code and/orrelated data may be stored on any type of computer readable medium suchas a storage device including a disk or hard drive or other storagemedium.

The computer readable medium may also include non-transitory computerreadable media such as computer-readable media that stores data forshort periods of time like register memory, processor cache, and randomaccess memory (RAM). The computer readable media may also includenon-transitory computer readable media that stores program code and/ordata for longer periods of time, such as secondary or persistent longterm storage, like read only memory (ROM), optical or magnetic disks,compact-disc read only memory (CD-ROM), for example. The computerreadable media may also be any other volatile or non-volatile storagesystems. A computer readable medium may be considered a computerreadable storage medium, for example, or a tangible storage device.

Moreover, a block that represents one or more information transmissionsmay correspond to information transmissions between software and/orhardware modules in the same physical device. However, other informationtransmissions may be between software modules and/or hardware modules indifferent physical devices.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims. Functionallyequivalent methods and apparatuses within the scope of the disclosure,in addition to those enumerated herein, will be apparent to thoseskilled in the art from the foregoing descriptions. Such modificationsand variations are intended to fall within the scope of the appendedclaims.

What is claimed is:
 1. A system comprising: a first sub-fleet ofballoons, wherein the first sub-fleet of balloons is assigned a firstset of one or more tasks within a balloon network; a second sub-fleet ofballoons, wherein the second sub-fleet of balloons is assigned a secondset of one or more tasks within the balloon network; and a controlsystem configured to: determine at a first time that a first balloon hasa first predicted failure mode that corresponds to the first set oftasks; based on determining that the first balloon has the firstpredicted failure mode that corresponds to the first set of tasks,assign the first balloon to the first sub-fleet of balloons; determineat a later second time that the first balloon has a second predictedfailure mode that corresponds to the second set of tasks, wherein thesecond predicted failure mode comprises a different type of predictedballoon failure than the first predicted failure mode; determine thatthe second predicted failure mode is more likely to occur earlier thanthe first predicted failure mode; and in response to determining thatthe second predicted failure mode is more likely to occur earlier thanthe first predicted failure mode, reassign the first balloon from thefirst sub-fleet of balloons to the second sub-fleet of balloons.
 2. Thesystem of claim 1, wherein the first sub-fleet of balloons operatesaccording to a first set of constraints; and wherein the secondsub-fleet of balloons operates according to a second set of constraints.3. The system of claim 1, wherein a predicted failure mode of a ballooncomprises a probability distribution of expected failure of the balloonover time.
 4. The system of claim 1, wherein the first balloon isreassigned from the first sub-fleet of balloons to the second sub-fleetof balloons after an initial time period during which the first balloonis exposed to one or more stress tests.
 5. The system of claim 1,wherein one of the sub-fleets of balloons is assigned to communicatewith one or more ground-based stations.
 6. The system of claim 1,wherein one of the sub-fleets of balloons is assigned to serve as relayballoons between other balloons within the network.
 7. The system ofclaim 1, wherein one of the sub-fleets of balloons is assigned to assistin weather forecasting.
 8. The system of claim 1, wherein one of thesub-fleets of balloons is assigned to travel along long-distance flightpaths.
 9. The system of claim 1, wherein the first predicted failuremode comprises a partial failure of a balloon system.
 10. The system ofclaim 1, wherein the first predicted failure mode comprises a predictedfailure of a first balloon component, wherein the second predictedfailure mode comprises a predicted failure mode of a second ballooncomponent, wherein the second balloon component is different than thefirst balloon component, and wherein the first balloon is reassignedfrom the first sub-fleet of balloons to the second sub-fleet of balloonsto reduce usage of the second balloon component.
 11. Acomputer-implemented method comprising: determining at a first time thata first balloon in a balloon network has a first predicted failure modethat corresponds to a first set of tasks, wherein the balloon networkcomprises at least a first sub-fleet of balloons and a second sub-fleetof balloons, wherein the first sub-fleet is assigned a first set of oneor more tasks and the second sub-fleet is assigned a second set of oneor more tasks; based on determining that the first balloon has the firstpredicted failure mode that corresponds to the first set of tasks,assigning the first balloon to the first sub-fleet of balloons;determining at a later second time that the first balloon has a secondpredicted failure mode that corresponds to the second set of tasks,wherein the second predicted failure mode comprises a different type ofpredicted balloon failure than the first predicted failure mode;determining that the second predicted failure mode is more likely tooccur earlier than the first predicted failure mode; and in response todetermining that the second predicted failure mode is more likely tooccur earlier than the first predicted failure mode, reassigning thefirst balloon from the first sub-fleet of balloons to the secondsub-fleet of balloons.
 12. The method of claim 11, further comprisingdetermining a first set of constraints and second set of constraints,wherein the first sub-fleet of balloons operates according to the firstset of constraints; and wherein the second sub-fleet of balloonsoperates according to the second set of constraints.
 13. The method ofclaim 11, wherein a predicted failure mode of a balloon comprises aprobability distribution of expected failure of the balloon over time.14. The method of claim 11, wherein the first balloon is reassigned fromthe first sub-fleet of balloons to the second sub-fleet of balloonsafter an initial time period during which the first balloon is exposedto one or more stress tests.
 15. The method of claim 11, wherein one ofthe sub-fleets of balloons is assigned to communicate with one or moreground-based stations.
 16. The method of claim 11, wherein one of thesub-fleets of balloons is assigned to serve as relay balloons betweenother balloons within the network.
 17. The method of claim 11, furthercomprising: determining at the first time that the first balloon has thefirst predicted failure mode based on sensor data from one or moresensors on the first balloon; and determining at the later second timethat the first balloon has the second predicted failure mode based onadditional sensor data from the one or more sensors on the firstballoon.
 18. The method of claim 11, further comprising: determining atthe later second time that the first balloon has the second predictedfailure mode based on one or more past failures of one or more otherballoons that performed at least some of the first set of one or moretasks assigned to the first sub-fleet of balloons.
 19. A systemcomprising: a plurality of sub-fleets of balloons, wherein eachsub-fleet of balloons is assigned a corresponding set of one or moretasks within a balloon network; and a control system configured to:determine that a first balloon initially has a first predicted failuremode that corresponds to a first set of tasks; based on determining thatthe first balloon has a first predicted failure mode that corresponds tothe first set of tasks, assign the first balloon to a first sub-fleet ofballoons that is assigned the first set of tasks within the balloonnetwork; periodically determine that the first balloon has a differentpredicted failure mode that corresponds to a set of tasks assigned to adifferent sub-fleet of balloons within the balloon network; determinethat the different predicted failure mode is more likely to occurearlier than any other previously determined failure mode; and inresponse to determining that the different predicted failure mode ismore likely to occur earlier than any other previously determinedfailure mode, reassign the first balloon to the different sub-fleet ofballoons.
 20. The system of claim 19, wherein the control system isfurther configured to: periodically determine that a certain sub-fleetof balloons has an inadequate number of balloons; and reassign one ormore balloons to the certain sub-fleet of balloons.
 21. The system ofclaim 19, wherein a particular set of tasks has a corresponding prioritylevel; and wherein at least one balloon is reassigned based on one ormore of the priority levels.
 22. The system of claim 19, wherein eachsub-fleet of balloons is operating within the balloon network accordingto a particular set of constraints.
 23. The system of claim 19, whereinat least one balloon is reassigned after an initial time period duringwhich the at least one balloon is exposed to one or more stress tests.24. A non-transitory computer readable storage medium having storedtherein instructions, that when executed by a computing device, causethe computing device to perform functions comprising: determining at afirst time that a first balloon in a balloon network has a firstpredicted failure mode that corresponds to a first set of tasks, whereinthe balloon network comprises at least a first sub-fleet of balloons anda second sub-fleet of balloons, wherein the first sub-fleet is assigneda first set of one or more tasks and the second sub-fleet is assigned asecond set of one or more tasks; based on determining that the firstballoon has the first predicted failure mode that corresponds to thefirst set of tasks, assigning the first balloon to the first sub-fleetof balloons; determining at a later second time that the first balloonhas a second predicted failure mode that corresponds to the second setof tasks, wherein the second predicted failure mode comprises adifferent type of predicted balloon failure than the first predictedfailure mode; determining that the second predicted failure mode is morelikely to occur earlier than the first predicted failure mode; and inresponse to determining that the second predicted failure mode is morelikely to occur earlier than the first predicted failure mode,reassigning the first balloon from the first sub-fleet of balloons tothe second sub-fleet of balloons.
 25. The non-transitory computerreadable storage medium of claim 24, wherein a predicted failure mode ofa balloon comprises a probability distribution of expected failure ofthe balloon over time.
 26. The non-transitory computer readable storagemedium of claim 24, wherein the first balloon is reassigned from thefirst sub-fleet of balloons to the second sub-fleet of balloons after aninitial time period during which the first balloon is exposed to one ormore stress tests.